1. Field of the Invention
The present invention relates to an organic electro luminescence (organic EL) display device having a high brightness and a long life.
2. Description of the Related Art
Recently, an electro luminescence (EL) element using a multi-layered film of an organic material attracts attention as disclosed in, for example, Jpn. Pat. Appln. KOKAI Publication No. 63-264692, Jpn. Pat. Appln. KOKAI Publication No. 63-295695, Jpn. Pat. Appln. KOKAI Publication No. 1-243393 and Jpn. Pat. Appln. KOKAI Publication No. 1-245087. Organic EL elements can be roughly classified into elements manufactured by a vacuum vapor deposition of a low molecular weight material, and elements manufactured by a polymer solution coating. The method employing the polymer solution coating facilitates the manufacture of an organic EL element having a large area and is adapted for, particularly, the manufacture of a large-screen, high precision, full color display using by the ink jet process.
In polymer organic EL display devices, an organic thin film having a thickness of scores of nanometers is required in order to lower the voltage applied to the display device. In addition, if the polymer thin film is nonuniform in thickness and poor in flatness within an element or among different elements, the pixel life is greatly reduced. Therefore, the polymer film is required to be uniform in thickness. Also, if the wettability within the nozzle is changed during the formation of the polymer film by the ink jet method, the uniformity of the pixels within the screen is greatly reduced. Therefore, the polymer solution is required to exhibit a consistent wettability in the film-forming process.
However, conventional organic EL display devices were not satisfactory in the thickness uniformity and the flatness of the polymer thin film within the element and among different elements. As a result, it was difficult to suppress the change in wettability within the nozzle in the step of forming a polymer thin film by the conventional ink jet method.